Los Angeles, CAImage fusion with HPET and CT currently has significant limitations for use in radiotherapy treatment planning according to a study being presented June 17 during the Instrumentation and Data Analysis session for nuclear technologists at the Society of Nuclear Medicine Meeting in Los Angeles. Designed to evaluate the co-registration accuracy of PET images transferred from a hybrid-PET gamma camera system (HPET) to a radiotherapy treatment planning system, the study used a phantom (i.e. simulated body) with heart, lung, and tumor inserts, and markers that would show up both on a CT, and because it used 18F, also on PET.

The phantom was scanned by the HPET system and by a CT scanner. The HPET images were transferred by DICOM (digital communication data transfer) to RTPS (a system for determining where and how much radiation therapy should be delivered)

The study found that while the CT and HPET images could be co-registered within 2mm in centrally located tumor inserts, tumor inserts on the peripheral was only 8-10mm, due to distortion and resolution lost of HPET images. In addition, markers and tumor inserts appeared larger on the HPET images than on the CT. The authors attributed this to settings on the RTPS that were compatible for the CT and not for PET. In addition, the authors found that the DICOM transfer truncated the maximum tumor pixel density in the HPET images, complicating edge definition of the tumors. As a result of their findings the authors determined that it would be difficult for a therapist to refine treatment volume using the co-registered HPET/CT images because the tumor edges on HPET images were not consistently defined, and because of image transfer issues between HPET and RTPS.

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Contact: Karen Lubieniecki
karenlub@aol.com
703-683-0357
Society of Nuclear Medicine
17-Jun-2002

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